If the site (your screenshot) doesn't list a custom image, then you may either check the vendor's web page to find out whether he offers a customized installation image, or go with the default VMware image.
from the vendor website (Installing VMware ESXi Installable, it direct me to vmware website to download the ESXi iso image but as you can see it is not listed in the screenshot i sent.
and what is the default VMware image and where can i find it ? does it work on most hardware ? or should i do something to prepare it in order to work on the oracle SUN server?
Since the vendor points to the VMware site, I assume that he's not providing a customized image. So what I'd suggest is that you register for the free Hypervisor Edition at Download VMware vSphere Hypervisor for Free, and see whether the installation works with the installation image you'll get from this link.
And also to provide some more relevant information, if the hardware you have still says "Sun" then it isn't supported on ESXi 6.5. Only those that came out after the Oracle name change are supported on ESXi 6.5.
